Method of making self-locking threaded element with locking patch effective over a wide range of clearances

ABSTRACT

Method of making a self-locking threaded element, e.g. a screw, including a strongly adhered plastic body or locking patch on its threaded surface where the locking patch is formed with a special configuration for effective locking engagement over a wide range of clearances between the element and mating threaded surfaces, in which method a stream of fine particles of heat softenable resin is directed against a threaded surface portion of a heated metallic element at a temperature lower than that effective to form a continuous convex curved deposit of resin. The threaded portion is kept in the stream of resin particles for a time sufficient to fill the valleys between threads to an extent of at least one-third in areas of the valleys adjacent the central line of the locking patch and to form thin resin deposits in areas spaced from the central line to give in effect an interupted ridge or bar useful to provide locking action over a wide range of clearances.

[ Jan. 22, 11974 THREADED ELEMENT WITH LOCKING PATCH EFFECTIVE OVER A ERANGE or CLEARANCES [75] Inventor: Richard J. Duffy, Salem, Mass.

[73] Assignee: USM Corporation, Flemington, NJ.

[22] Filed: Nov. 30, 1971 [21] Appl. No.: 203,130

[52] US. Cl. 117/21, 10/10 R, 10/10 P, 151/7 [51] Int. Cl B44d 1/94 [58]Field of Search... 117/21; 151/7; 10/10 R, 10 P [56] References CitedUNITED STATES PATENTS 3,498,352 3/1970 3,579,684 5/1971 Duffy 10/10 P3,554,258 1/1971 Duffy 117/21 X 3,294,139 12/1966 Preziosi 151/73,634,577 1/1972 Kull 151/7 X 2,928,446 3/1960 James et a1. 151/73,061,455 10/1962 Anthony 151/7 3,093,177 6/1963 Villo 151/7 3,263,7268/1966 McKay 151/7 3,568,746 3/1971 Faroni et al. 151/7 PrimaryExaminerWi11iam D. Martin Assistant Examiner-Shrive P. Beck Attorney,Agent, or Firm-Richard B. Megley et al.

[5 7] ABSTRACT Method of making a self-locking threaded element, e.g. ascrew, including a strongly adhered plastic body or locking patch on itsthreaded surface where the locking patch is formed with a specialconfiguration for effective locking engagement over a wide range ofclearances between the element and mating threaded surfaces, in whichmethod a stream of fine particles of heat softenable resin is directedagainst a threaded surface portion of a heated metallic element at atemperature lower than that effective to form a continuous convex curveddeposit of resin. The threaded portion is kept in the stream of resinparticles for a time sufficient to fill the valleys between threads toan extent of at least one-third in areas of the valleys adjacent thecentral line of the locking patch and to form thin resin deposits inareas spaced from the central line to give in effect an'interupted ridgeor bar useful to provide locking action over a wide range of clearances.

5 Claims, 9 Drawing Figures PATENTED JAN 2 2 59M SHEEI 2 BF 2 METHOD OF1 u SELF-LOCIKWG THREADED ELEWNT WITH LOCKMG PATCH EFFECTIVE OVER A WIDERANGE OF CLEARANCES BACKGROUND OF THE INVENTION 1. Field of theInvention This-invention relates to improvements in methods of makingself-locking threaded elements.

1. Description of the Prior Art In my prior US. Pat. No. 3,498,352,entitled Selflocking Threaded Element which issued Mar. 3, 1970,

ing smoothly from one axially extending edge of the patch to theopposite edge of the patch and with smoothly changing thickness of thepatch from a maximum thickness midway between the longitudinal edges tominimum thickness adjacent the edges. Ordinarily, the deposit of plasticis so uniform as not greatly to alter the thread appearance.

Self-locking threaded fasteners with looking patches, prepared inaccordance with my prior patent, have been eminently satisfactory formost uses and the invention has gone into extensive commercial use.However, the clearance between the surfaces of an external screw threadand a mating internal screw thread particularly with "the lower class ofthread fit may vary to such an extent that where, for example, theexternal screw threaded member is at the lower range of allowablemanufacturing tolerance and the internal screw threaded member is at theupper end of the range of allowable tolerance, the normal self-lockingpatch may provide insufficient locking torque, while with another pairof mating screw threaded members where the external screw threadedmember is at the upper end of the allowable manufacturing tolerance andthe internal screw threaded member is at the lower end of the allowabletolerance, excessive torque may be required for installation and removalof the threaded members.

It is an object of the present invention to provide a self-lockingelement providing effective locking action between mating threadedmembers having relatively large variations from normal size.

To this end and in accordance with a feature of the present invention Ihave provided a method of making a self-locking threaded fastenerelement including a strongly adhered plastic body having a specialconfiguration which provides effective locking action between threadedmembers even those having large variations from nominal size.

BREIF DESCRIPTION OF THE DRAWINGS The invention will be describedfurther in connection with the attached drawings in which:

FIG. 1 is an angular view of one form of self-locking threaded fastenerelement in accordance with the present invention;

FIG. 2 is a cross-sectional view on a larger scale on the line ll-II ofFIG. 1;

FIG. 3 is a cross-sectional view on a larger scale on the line Ill-IIIof FIG. ll;

FIG. 4 is a fragmentary view in longitudinal section on a much largerscale taken on the line lV-IV of FIG. 2 showing the distribution of theplastic material on the threads of the fastener element near one edge onthe plastic deposit;

FIG. 5 is a fragmentary view in longitudinal section on a much largerscale taken on the line VV of FIG. 2 showing the distribution of theplastic material on the threads of the fastener element intermediate ofthe longitudinal edge and the longitudinal center line of the plasticdeposit.

FIG. 6 is a fragmentary view in longitudinal section on a much largerscale taken on the line VI-'-VI on FIG. 2 showing the distribution ofthe plastic material on the threads of the fastener at the longitudinalcenter line of the plastic deposit;

FIG. 7 is a diagrammatic elevational view illustrating apparatus usefulfor forming a plastic deposit on the threaded surface;

FIG. 8 is a diagram, similar to a cross-sectional view, of a threadedfastener element for purposes of explaining the angles at which resinparticles from a stream of resin particles strike the threaded surface;and

FIG. 9 is a diagram, similar to an angular crosssectional view, of athreaded fastener element for purposes of explaining the angles at whichthe resin particles, from a stream of resin particles, strike thehelical bearing surfaces of a threaded member.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will be describedin relation to providing a self-locking plastic body on a threaded bolt,but it is to be understood that it is useful in providing a selflockingbody on threaded portions of other articles.

A locking-type threaded element 10 shown as a bolt (see FIG. 1)according to the present invention carries an integral continuousdeposit or body 12 of tough, resilient resin formed in situ on aselected area of the normal threaded surface 14 of the threaded elementby deposition and fusion of fine particles of thermoplastic resin on aheated surface of the threaded element. A film of primer or tyingmaterial (not .shown) may be provided on the selected area on thesurface of the threaded element to aid in deposition of the plasticparticles in the course of making and to give superior adhesion betweenthe surface and the resin body.

The resin body 12 covers portions of the valley 16, the inclined helicalbearing surfaces 18 and the crests 20 of the threaded surface 141 and isso located as to be compressed between the threaded surface 14 of theelement l0 and mating threads of a complementary element with which thethreaded element is assembled to provide increased frictional resistanceto undesired loosening of the threaded engagement between the threadedelement and the complementary element.

As shown in FIGS. 1 to 6 the resin body includes a thin coating layer 22on the axially extending side portions of the body and substantiallythicker central portions 24 in the valleys 16 between threads. Thiscentral portion 24 increases rather abruptly in thickness, as shown inFIG. 2, from the general thickness of the coatings 22 on the sideportions to a thickness at least about 50 per cent greater than thethickness which would be reached if the surface curved smoothly asextensions of the curves generated by the surface of the resin in theside portions along the center line of the valley (note the broken linein FIG. 2). The broken line may be considered as a line interpolatedfrom the curvature of the surface of the resin on the side portionsalong the center line of the valley. A further characterization of theabruptness of increase of the thickness of the resin body in the valleyis that the radius of curvature R in central portions 24 of the resinbody 12 is actually smaller than the radius of curvature Rv of thesurface of the threaded element along the center line of the valley.

Thicker central portions 24 are disposed in the valleys 16 throughoutthe axial length of the resin body and may be regarded as constituting aridge interrupted by the crests 20 of the threads. It will be understoodthat the crests 20 themselves have at least a thin coating of resin (seeFIGS. 3 to 6) and that an amount of resin may be deposited on thethreaded element such that the higher portions of the ridge extend overthe crests of the threads.

This special configuration of resin body is particularly important forgiving self-locking action between complementary screw threads where awide range of clearance may be encountered. That is, where there is alarge clearance between the external screw threaded member and theinternal screw threaded member, the thickness of the central portion 24of the resin body 12 in the valleys 16 is adequate to press against themating screw threads with sufficient force to prevent undesiredloosening of the engagement between theaded members. On the other hand,where the clearance between the internal and external screw threadedmembers is small, the relatively small circumferential extent of thecentral portion 24 permits the resin to be distorted between internaland external screw threads and in the case of very low clearance to bewiped over into a thinly coated side portion 22 of the resin deposit 12.An important feature of the resin patch of particular value where theclearance is low is that the side portions 22 of the resin body firmlyanchor the thicker central portion 24 against displacement from thethreaded surface 14 without materially increasing the torque requiredfor installation.

The process of making such locking type fasteners will be described asit is practiced using the apparatus diagrammatically shown in FIG. 7,but it will be understood that other apparatus than that shown may beused, or the process may be carried out by hand. In the apparatus,threaded fastener elements shown as threaded members are conveyed on acarrier through the successive steps of the process. The carrierincludes spaced parallel endless belt members 26 traveling on pulleywheels 28 and 30. The threaded members preferably are suspended invertical position with portions of the heads 32 resting on the spacedparallel moving belt members 26 with depending portions exposed fortreatment.

The threaded surface 14 may be given a primer coat either before orafter positioning on the carrier. If such coating is applied, anysolvent in the primer is evaporated before the threaded fasteners arecarried to a heating station. The heating station may be an oven, butpreferably is a high-frequency field heating unit 34 designed to heat asuccession of threaded members 10 moving continuously past it on thecarrier. As shown in the drawing, the coil of the heating unit 34 iselongated in the direction of movement of the threaded members on thecarrier to provide adequate heating time to raise the threaded membersto the desired temperature. From the heating station the threadedmembers 10 are next moved to a station at which fine plastic particlesare applied. At this station, fine plastic particles suitably as auniform stream 36 in a jet of gas such as air, are directed at theheated threaded members 10 from a jet nozzle 38 which provides arelatively wide, preferably substantially parallel edge stream throughwhich the threaded members 10 are moved. The dimensions of the nozzle 38in the direction of movement of the threaded members 10 are chosen tocontrol the time during which a member 10 on the carrier is subjected toa stream of particles and the vertical dimension of the nozzle is chosento provide the desired axial length of resin deposited on the member.The particles applied are not confined or restrained by a mold or othershaping device but are freely movable into engagement with the crests,helical bearing surfaces and valleys of the threaded surfaces of thethreaded members. Because of this fact, the particles deposit a layer ina desirable relationship to the threaded surface both to allow easyinstallation, i.e., assemblywith a complementary threaded element, andstrong holding power on the first and subsequent uses. The velocity ofthe particles in the stream should be kept in the range of about l to 25ft. per second for deposition on the threaded members. Particles arecaught and held on the hot surface and are then fused to a continuouscoherent mass by the sensible heat of the threaded members 10. When thethreaded members 10 and body 12 of plastic material have cooled, theplastic is in the form of a coherent, tough, resilient patch coveringcrests 20, sides 18, and valleys 16 of the threaded surface.

The procedure is similar to the procedure forming the subject matter ofmy prior U.S. Pat. No. 3,579,684; but to secure the specialconfiguration of resin body certain changes from the procedure of thatpatent are used to give the new configuration.

That is, for effective development of a ridged configuration, thetemperature of the threaded member at the time the stream of particlesis directed against it will be below the minimum temperature at whichthe continuously convex curved locking bodies are formed, preferably atleast about 20 F. below that temperature. The term continuously convexcurved as employed herein refers to a curve in which the rate of changeof curvature of the surface is substantially continuous on each side ofthe center line of the bodies. Also, it has been found that finerparticle size and higher melt viscosity resin than normally employed tomake the usual resin body are important to aid in the formation of thenew configuration resin deposit.

The novel configuration of the resin body 12 including the ridgedcentral portion 24 is apparently the result of a factor which was maskedby the conditions of earlier operations. That is, in the formation oflocking resin deposits as heretofore known, resin particles striking onthe very hot surface, adhered and melted through almost immediately sothat further particles would adhere to the melted resin material and thedeposited resin would form a layer smoothly varying in thickness from aminimum at the edges to a maximum at the center.

But, under the conditions used according to the present invention,particles are not as readily caught and do not melt through so rapidly;and a valley effect appears which produces the novel ridgedconfiguration.

The action may be understood better by reference to the diagrammaticFIGS. 8 and 9 in which lines 40, 42 and 44 represent the paths ofparticles in the stream of particles striking the thread surface at thecentral line, at an intermediate portion and near an edge portion of thethreaded surface I4 as viewed from the direction of the stream ofparticles 36. At the side portion along line 44, the helical bearingsurfaces 18 of the threads are at only a slight angle to the path of theparticles in the stream due to the fact that the aspect of the thread asshown in FIG. 9 presents only a small angle and the further fact thatthe path of the particles is nearly tangent to the threaded surface asshown in FIG. 8. Accordingly, the component of movement towards thethreaded surface is small while the component tending to sweep theparticle past the threaded surface is high so that build up of resin isslow and only a thin deposit of resin is formed on the helical surfaceas shown in FIG. 4. Particles traveling along the midpoint line 42 andalong the central line 40 strike the helical bearing surface is at thesomewhat greater angles 50 and 52 and therefore, have a somewhat greaterchance of being caught and held to form thicker resin deposits as shownin FIGS. and 6. With all of these areas, the chance of particlesbeingcaught and held on the crests 20 and helical bearing surface 18increases with the temperature of the threaded element so that, athigher temperatures within the desired range, there will beprogressively greater thickness of resin from a minimum at the sides toa maximum at the central line.

A further factor of importance in determining the build up is the use ofvery fine particles of resin. The particles should be less than 600microns and particle size less than 400 microns is preferred. Bestresults have been obtained with particles in the range of to 200microns. The fineness of the particles tend to emphasize the depositionbehavior discussed above. That is, the ratio of surface area to weightof the resin particles varies inversely as the diameter. Accordingly,the finer particles tend to remain in the stream of air flowing past thethreaded surface and this effect is much more pronounced at the sideportions than in the central portions so that the relative amount ofresin deposited on the central portion to the amount deposited on theside portions is greater with the finer resin particles.

It has always been found that relatively lower particle velocitiesemphasize the desired deposition behavior. This factor is particularlyuseful where particles of the larger sizes in the useful range are to beemployed.

The valley effect," referred to above, results from the fact that at thebases of the valleys 116 between threads, the particles cannot slideaway as they can from the crest and helical bearing surfaces 1%. Thus,as shown in FIG. 8, the surface of the base of the valley I6 at thecentral line 40 of the threaded element as viewed from the direction ofthe stream of particles 36 is at a right angle 54 to the stream 36 andprovides maximum particle collecting ability. In this area, the firstparticles striking the surface are caught and adhered to the hotsurface; but further resin particles have been observed to pile up onthose hot resin particles at a rate faster than they are melted. Smallerparticles pile up more effectively than the larger particles and alsoform a more uniform body of resin after the pile is melted and cooled.At the-midpoint along line 42, the angle 56 between the stream 36 andthe surface of the base of the valley I6 is somewhat greater so that theability to collect particles is somewhat less than along the centralline 44 but is still substantially greater than the ability of thecorresponding helical bearing surface llfirParticles traveling along theline at the edge of the threaded surface are nearly tangential to thethreaded surface, approaching the surface at the very small angle 58,and have very little chance of being caught and held. The net effect ofthis is a variation in ability to catch and hold particles so that theparticles collect rapidly at the bases of the valleys 16 along thecentral line 40 and this ability falls off sharply away-from the centralline so that a deposit builds up in areas near the central line 40.Also, the particles deposited along the bases of the valleys 16 areheated by the hot walls 18 on both sides of the valleys so that theparticles are melted rapidly to catch and hold further particles. Buildup of resin in the valleys 16 provides a surface of resin which does nothave the angled aspect of the helical bearing surfaces so that the resinbuilds up progressively in the central portion to form a ridged depositinterrupted by the crests of the threads.

It is to be understood that the above discussion is given to aid inunderstanding the invention and that patentability is not based upon thecorrectness of the explanation advanced.

Primers or tying coats-which may be applied to the threaded surface toaid in trapping particles from the stream directed against it may be anyof a wide variety of heat-softenable resin materials such, for example,as polyamide resins, epoxy resins, resorcinol aldehyde resins andcombinations of these. The primer or tying agent may be applied to thethreaded surface in a volatile solvent solution. For example, a 10percent solids solution of an alcohol-solution nylon in denaturedalcohol gives good results.

The locking bodies or patches are formed of tough, resilient,heat-softenable resin material. Polyamide polyester and polyurethaneresins have been found particularly useful and a preferred polyamideresin in nylon II. The resin materials are applied in the form of fineparticles. The size of the particles to be used depends to some extenton the size of the threaded element to which the patch is to be applied.The smaller the threaded element, the smaller the particles desired. Fora inch threaded element, a useful range of particle sizes is such thatonly about 2 percent would be retained on a No. 140 sieve.

It has also been found that an effective primer for combination with theresin of the locking deposit may be obtained using a powder mixtureformed by combining a minor proportion, i.e., from about 5 percent toabout 35 percent by weight of particles of a primer or tying agent suchas the resin materials above noted, with a major portion, i.e., fromabout percent to about 65 percent by weight of particles of the resinmaterial which makes up the main body of the locking deposit, bothpercentages being on the weight of the powder mixture. It appears thatthe primer or tying material fuses at a lower temperature than does theresin material and also that it is more fluid and more capable ofwetting the threaded surface so that the heat of the threaded membercauses it to fuse and flow into wetting engagement 'with the threadedsurface to provide the desired primer and tying action.

In forming locking deposits on threaded surfaces, the temperatureselected will be governed by the softening or melting temperatures ofthe primer or tying material where used and of the primary resinmaterial. Where the powdered resin is the polyamide, nylon 11, which hasa melting point of about 367 F., temperatures in the range of from about450 F. to about 575 F. have been found satisfactory. It is desirablethat the temperature to which the threaded members are heated be suchthat the sensible heat is sufficient to keep the temperature of thethreaded members above about 400 F. for at least about seconds.

In heating of the threaded member, for example, a bolt 10, by a highfrequency electric field, for example, at a frequency of 450 kilocycles,a steel threaded bolt can be brought to the desired temperature in from2 to 3 seconds. In a continuous process, the threaded elements may bepassed through the high frequency field at a rate providing the desiredheating time.

The overall thickness of the resin body is controllable by the natureand rate of supply of particles in the stream, by the temperature of thethreaded element and by the time the threaded element remains in thestream of particles. As noted previously, the thickness of the centralportion is the primary factor of importance and it is desirable thatthis portion have a thickness measured at the center line of at leastone-third and preferably not more than about the full depth of thevalley between threads.

tween the belts leaving the portions to be coated exposed as shown inFIG. 7. A thin layer of primer solution was deposited on exposedportions of the screws on which plastic patches were to be formed. Theprimer was a 10 percent solids solution in alcohol of an alcohol solublenylon and an epoxy resin in a ratio of solids of 1:2 parts by weight.The deposited material on the screws was dried leaving very thinsubstantially continuous primer coats. The screws 10 were then conveyedin proximity to a high-frequency field coil 34 operating at a frequecnyof about 450 kc. with a power source of 2 kw. capacity.

The time in which the screws 10 were in the high frequency field wascontrolled to produce the temperatures shown in the table below.Directly thereafter, the screws 10 were moved by the belts 26 so thatthe primer coated areas of the screws pass through a laterally directedstream 36 of powdered resin. The heatsoftenable primer layer on thesurface of the screws caught and held powder particles and the powderparticles were fused by heat by the screws to form adherent plasticpatches.

After cooling, the plastic patches were smooth, hard, and firmlyadherent. The screws were assembled with nuts and measurements were madeof the maximum initial installation torque and of minimum removal torquefor the first, fifth, and fifteenth removal of the screws from the nuts.The results are listed in the following table.

Temperature of Material Resin for Locking Initial Installation MinimumRemoval Torque (inch-pounds) screw when resin Patch (resinTorqueMaxapplied particles size in imum microns) (inch-pounds) lst 5th15th 550F. Thermoplastic IO 35 25 23 polyurethane resin melting point428F.

580F. Polyamide 100-600 25 25 20 While as described above, the plasticparticles are applied by moving the heated threaded element through asingle stream of particles, it will be understood that EXAMPLE In thisexample, the screws were of steel of black oxide finish and had a screwsize of 5/16 inch -18 UNC 2; and the nuts were of steel with a cadmiumplating and had a screw size of 5/16 inch l8 UNC 3.

The screws 10 were disposed with their enlarged head portions 32 restingon the two moving belts 26 and with the threaded portions 14 extendingdown be:

It was observed that where the temperatures of the screws was brought to600 F. before the screws passed through the stream of resin particles, acoating was formed about 0.004 inch in thickness along its center lineand tapering smoothly to the axially extending edges of the bodies. Withthe polyamide resin particles, where the screws were heated to atemperature of 580 F very thin coatings on the side portions wereformed; but the central area developed a ridge of which the surface roseabruptly from the surface coating on the side portions to reach athickness in the valleys along the center line to fill the valleys toabout three-fourths of the depth of the valleys. I

Where the very fine particle size resin was used and the temperature ofthe screws was only 550 F. at the time of contact with the stream ofresin particles, a thin coating was formed on the side portions and acentral ridge was formed even more marked than that formed by thepolyamide resin. It is noted that with the finer particles, although theinstallation torque was somewhat higher than that of the locking patchesformed with the somewhat coarser resin, the removal torque was very highand fell off only slightly in successive removals.

Having thus described my invention what I claim as new and desire tosecure by letters Patent of the United States is: k

1. In a method of providing a threaded portion of an article with aself-locking element comprising an adhered body of normally hard, tough,resilient thermoplastic resin, said method including the steps ofheating the threaded portion to a temperature above the softening pointof said resin, thereafter, directing a stream of fine particles of saidresin at a selected area of said threaded portion while said threadedportion is at a temperature above said softening point, catching resinparticles from said stream by softening them and causing them to adhereto said threaded portion by heat from said threaded portionprogressively to build up a deposit of said resin, fusing adheredparticles to coalesce them to a substantially continuous body of resin,and cooling said body of resin to harden it to a solid body resistant todisplacement and effective to give a locking action when a complementarythread member is assembled with said threaded portion, the improvementin which said resin particles have a size less than 600 microns, thetemperature of the threaded portion when exposed to said stream of resinparticles is at least about 20 F. below the minimum temperatureeffective to form a continuously convex curved deposit of resin fromsaid stream of particles, and gives a low rate of build up of resindeposit on the helical bearing surfaces and crests of said threadsrelative to the rate of build up of resin deposit at the base of saidvalleys in areas adjacent the central line of the threaded portion takenfrom the direction of said stream of particles, and said threadedportion remains in said stream of resin particles for a timesufiicientto fill areas of said valleys adja:

cent said central line to an extent of from about onethird up to aboutthe full depth whereby, deposited resin forms thin side portions andforms thicker portions in said valleys in areas adjacent said centralline, the surfaces of said thicker portions rising abruptly above linesinterpolated from the curvature of the surface of the resin on said sideportions, the radius of curvature of the surface of said thickerportions in the planes approximately including the center lines of thebase of the valleys being smaller than the radius of curvature in saidplanes at the thread surface.

2. The method of providing a self-locking element as defined in claim 1in which said threaded portion is brought to a temperature which willremain above about 400 F. for at least about 5 seconds after firstcontact with said stream of resin particles and said resin particleshave a particle size of less than 400 microns.

3. The method of providing a self-locking element as defined in claim 2in which said resin particles have a size of from 10 to 200 microns.

4. The method of providing a self-locking element as defined in claim 2in which a resin primer coat is disposed on the surface of said threadedportion before heating said threaded portion.

5. The method of providing a self-locking element as defined in claim 2in which said stream is a mixture of a major portion of fine particlesof said normally hard thermoplastic and a minor portion of aheat-softenable tying agent, and said tying agent is fused on thesurface tron.

2. The method of providing a self-locking element as defined in claim 1in which said threaded portion is brought to a temperature which willremain above about 400* F. for at least about 5 seconds after firstcontact with said stream of resin particles and said resin particleshave a particle size of less than 400 microns.
 3. The method ofproviding a self-locking element as defined in claim 2 in which saidresin particles have a size of from 10 to 200 microns.
 4. The method ofproviding a self-locking element as defined in claim 2 in which a resinprimer coat is disposed on the surface of said threaded portion beforeheating said threaded portion.
 5. The method of providing a self-lockingelement as defined in claim 2 in which said stream is a mixture of amajor portion of fine particles of said normally hard thermoplastic anda minor portion of a heat-softenable tying agent, and said tying agentis fused on the surface of said threaded portion by heat from thesurface of said threaded portion to wet said portion and to aid inbuilding up and adhere deposits of said normally hard thermoplasticresin on the surface of said threaded portion.